The invention relates to a fastener comprised of an at least in part axially extending externally threaded shaft and a driving head adjoining the trailing end facing opposite the leading end to be inserted first into a structure, the driving head has on its side facing toward the leading end a plurality of radially extending, separated webs spaced outwardly from the axis of the shaft up to the external circumferential edge of the side facing toward the leading end. The webs have an essentially trapezoidal cross section limited by a face surface directed toward the leading end and two flank surfaces.
Fasteners of the type described above are used not only in construction but find use in many other areas such as vehicle construction, component construction and the like. Webs situated on the side of the driving head facing in the insertion direction serve to secure the fastener against unintended loosening. Particularly in applications in which the fastener is exposed to strong vibration, for example in a vehicle or machine, the webs prevent unintended loosening of the connection established by the fastener.
U.S. Pat. No. 3,640,326 discloses such a fastener formed of a shaft and a connected driving head on the end facing away from the insertion direction. On its side facing in the insertion direction a plurality of separate webs are arranged extending radially from the axis of the shaft up to the radially outer edge of the side. The webs have an essentially trapezoidal cross-section.
The advantage of the known fastener consists in that at the time of tightening the fastener to a structural part for example, the webs at least partially penetrate into the surface of the structural part and consequently establish a positive form locking and a friction-locking connection in the insertion or setting direction between the driving head and the structural part, by virtue of which the fastener is secured against unintended loosening.
The drawback of the known fastener is the fact that at the time of tightening the fastener to a surface, for example, the head is subjected to a very high torque and this results in a twisting off of the head from the shaft; particularly in situations in which a motor-driven screwdriver device is used there is the risk of excessive turning between the driving head and the shaft.
The primary object of the present invention is to create a fastener that is resistant to excessive twisting forces. Moreover, the fastener is resistant to unintended loosening, and is secured against unintended loosening.
The object is achieved according to the invention in that the radially extending space between the flank surfaces of two adjacent webs is constant over their entire radial extent.
By virtue of the fact that the spacing of the flank surfaces is constant the face surfaces of the webs increase with increasing distance from the axis of the shaft and consequently also the friction surface, since the face surfaces of the webs are configured in segments. By varying the total surface of all of the webs arranged on the side facing in the insertion or setting direction the configuration of the maximum tightening torque can be defined. This results in the creation of a safety device, that prevents twisting off of the driving head from the shaft, particularly when using motor-driven screw driving devices. Furthermore, for example, it is possible to configure the face surface of the webs in different sizes and structures for fasteners for use with different receiving materials such as, for example, concrete, wood, or plastic and so, for example, prevent destruction of the connection by over-tightening a shaft in the bore hole.
The webs advantageously exhibit, on the external circumference, a width extending in the peripheral direction that corresponds approximately to the circumferential space of the lateral or flank surfaces of two adjacent webs to the effect of creating a large face surface of the webs, which, when tightening the fastener in, for example, a component, results in high friction between the driving head, in particular the webs on the underside of the driving head, with the surface of a structural component or receiving material.
Preferably the two corresponding flank surfaces of a web include a base angle of approximately 90xc2x0 to assure optimum penetration into the surface.
Advantageously, the face surface runs perpendicularly to the axis of the shaft so that the surface is not heavily damaged by engagement of the webs. Thus, on the one hand splitting of the surface is prevented and on the other hand foreseeable basic conditions are assured.
The webs have a height h extending preferably in the setting direction relative to the underside of the driving head that corresponds to 0.009 to 0.015 times the external diameter of the underside in order to assure optimum frictional characteristics.
To prevent premature erosion of the webs into the surface the radially extending edges formed by the corresponding flank surfaces and face surfaces are advantageously rounded. This further prevents unnecessary cutting away of material from the surface of the structural component or receiving material by the rotating webs of the driving head.
In order to assure optimal fastening behavior, adjacent webs are advantageously arranged transverse to the shaft axis by an angle of 5xc2x0 to 10xc2x0 relative to each other.
The spacing of the webs radially outwardly from the shaft corresponds in a preferred embodiment to 0.3 to 0.4 times the external diameter of the underside in order to prevent premature engagement of the webs in the region of the shaft, since at the surface in the region of the shaft, for example, material of the structural component is present that is cut away from it by the shaft.